At the same time as politicians and the business community are trumpeting mining as a "new Nokia" for Finland, some areas are still seeing the impact of the last mining boom in the 20th century.

The effects on the environment are evident, for example at Outokumpu in North Karelia, which was the site of what was probably the most significant mining complex in Finland's past. A memento of those times is the high levels of sulphate, iron and manganese in the groundwater that makes it unusable in large parts of the city of Outokumpu.

It has come as a surprise to many that the source of the biggest sulphate emissions in the region of North Karelia is the Hammaslahti mine, a facility that was closed down almost 30 years ago. According to the North Karelia Centre for Economic Development, Transport and the Environment, every 24 hours 1.5 tonnes of sulphate flow out of the old mine into the Iiksenjoki river. As a result, the acidity of river waters is rising.

Increased micro-organisms

At Hammaslahti, corrective measures are being carried out by the company that owned and operated the mine. In cases where a mine has been abandoned, it is the local government or the state that pays the bill.

According to the latest survey, there may be dozens of closed or abandoned mines that are releasing waters tainted by acids and metals. The survey was jointly carried out by Finland's Environmental Administration, the Geological Survey of Finland, and the Kainuu Centre for Economic Development, Transport and the Environment.

The Geological Survey says that complaints have been received of effects such as strong, unpleasant smells from lakes that indicate a depletion of oxygen in the waters. Often, emissions from old mines increase the activity of micro-organisms that is spurred by the minerals released by crushed rock and can continue for hundreds of years.

The same thing is to be seen in North America, where purification plants have had to be built to deal with waters leaking from mines closed in the 1800s.

Unresolved issues

Dealing with the problem is not a simple matter, and in some cases, for example at Hammaslahti, corrective measures may have actually increased the damage.

Environmental rules today are a lot stricter in Finland than they were during the last mining boom during the 20th century, but new technologies mean that less concentrated deposits can be mined. That also means massively more waste.

For example, when the Talvivaara mining site at Sotkamo is closed, it will leave behind a two square kilometre area covered by mounds 50-60 metres in height. There is a risk that they will contribute to acidity and the proliferation of micro-organisms in local waters.

Officials say that the details of post-operations treatment of the mining site will not be worked out until closer to the time that the mine is closed down.

Company plans now are for the mounds of mining waste to be covered with plastic sheeting. According to Sami Koivula, the director for environmental permit affairs for the regional administration of North Finland, some kind of arrangements for runoff water will have to be maintained for centuries.

"These plastic elements will not, of course, last forever. The manufactures promise a lifespan of several centuries, but it is not eternal," Koivula points out.

The next question may be whether or not the guarantees paid by mining companies will really be enough cover the costs of the follow-up.